Loud speaker system



March 1953 J. E. PARKER LOUD SPEAKER SYSTEM 2 SHEETS-SHEET 1 Filed April18 1949 JOHN E. PARKE/2 flT'TORNEY A/olzM/aL SPEAKER REJPONJE F I E 5Patented Mar. 17,; 1953 UNITED STATES PATENT OFFICE LOUD SPEAKER SYSTEMJohn E. Parker, Great Falls, Mont.

Application April 18, 1949, Serial No. 88,152

Claims. 1

This invention relates to loud speaker systems, and more particularly tosystems employing multiple loud speaker units.

A main object of the invention is to provide a novel and improved loudspeaker system which involves very simple components, provides accurateresponse, especially of low frequency tones, and which has very lowintermodulation distortion.

A further object of the invention is to provide .an improved loudspeaker system which will reproduce fundamental tones as low as 20cycles per second and which has a substantially flat response down tothis low frequency, without the usual low frequency resonant peaks whichare present when all the speaker units are operated above as well asbelow their resonant frequencies.

A still further object of the invention is to provide an improved loudspeaker system which will reproduce very low frequency tones without theuse of large cabinets or baflles, the system embodying the use ofseparate speakers of relatively small size for reproducing low tones,said speakers being operated below their natural resonant frequenciesinstead of above.

A still further object of the invention is to provide an improved loudspeaker system of the type employing multiple speakers, wherein separatespeaker units are employed for reproducing low frequency tones, each ofthe low frequency speakers being, in effect operated only below itsnatural mechanical resonant frequency, and wherein the operating rangeof the low frequency speaker units is also below their electricalresonance frequencies and below the resonance frequencies of the speakerenclosures.

A still further object of the invention is to provide an improved loudspeaker system of the type employing multiple speakers and whereinseparate speaker units are employed for reproducing low frequency tones,the speaker units being arranged in groups or cells in honeycombfashion, and wherein a composite speaker is provided which has a highefficiency, has smooth low frequency response, and occupies only a smallamount of space. 1 Further objects and advantages of the invention willbecome apparent from the following description and claims, and from theaccompanying drawings, wherein:

Figure 1 is a perspective view of a composite loud speaker assemblyconstructed in accordance with the present invention.

. Figure 2 is a perspective view of a single cellular speaker element,

Figure 3 is a horizontal cross-sectional view taken on line 3-3 ofFigure 1.

Figure 4 is a vertical cross-sectional view taken on line 44 of Figure1.

Figure 5 is a chart representing graphically the normal response of acomposite speaker assembly comprising a group of cellular units of thetype illustrated in Figure 2, when arranged in the manner shown inFigure 1.

Figure 6 is a chart showing the response curve of a low frequencyamplifier adapted to drive the low frequency speaker elements of aspeaker system constructed in accordance with the present invention.

Figure '7 is a block diagram illustrating the electrical relationshipsof the various portions of a loud speaker system constructed accordingto this invention.

Figure 8 is a perspective view of a modified composite speaker assemblyaccording to the present invention.

Figure 9 is a perspective view of another composite speaker assemblyaccording to the present invention.

Figure 10 is a perspective view illustrating still another compositespeaker assembly in accordance with this invention.

Figure 11 is a perspective view showing a pair of composite speakerassemblie which are constructed in accordance with the presentinvention, said assemblies being spaced apart physically but cooperatingto produce improved low frequency reproduction in a given room or audi:torium'.

Referring to the drawings, and more particu larly to Figures 1 to 4, lldesignates a cabinet, which, by way of example, is shown as beingrectangular, and which is divided up into individual cells or enclosuresby means of vertical partit1on walls l2 and horizontal partition wallsI3. The cabinet II has a rear wall 14. Each of said cells contains asmall loud speaker unit l5, suit:- ably mounted on a bailie board l6secured to the forward margins of the walls of the cell.

The structure of Figures 1, 3 and 4 may be built up of individualbox-like units, suchas shown at I! in Figure 2. The speaker units may bearranged in the manner shown in Figure .1 or may have other arrangementssuch as those to be subsequently described.

Figure 5 is a graph illustrating the normal re! sponse of conventionalsmall speaker units such as shown in Figure 2, when operated in smallgroups arranged in the manner shown generally in Figures 1, 3, 4 and inthe other figures, such 3 as Figures 8 and 9. From Figure 5, it will beseen that the response has a definite peak or maximum in theneighborhood of 200 cycles per second, the response dropping oif sharplybelow this point, and the response above this point being more or lessfiat. This means that where all of the speakers of the assembly carrythe same range of frequencies and are driven from an ordinary amplifierhaving substantially fiat output, the sound output of the system willhave a peak or resonance point in the neighborhood of 200 cycles,thereby producin a definite low fre-, quency distortion effect whereintones in the neighborhood of 200 cycles per second will appear to beaccentuated. The resonance point will shift downwardly or upwardlydepending upon whether more or less cellular units are employed in theassembly and also depending upon the manner in which the units aredistributed and on the size and type of units employed.

The above described resonance effect is ordinarily due to the naturalmechanical resonance ofthe speakers (resulting from the combination ofcone or diaphragm and associated suspension conditions) to which may beadded the electrical resonance of the speakers and the resonance of thespeaker enclosures. Where small speaker units (andsmall cells) areemployed, as above described, the resonance frequencies of the assemblyare relatively high. For example, employing five-inch speakers insix-inch cubical enclosures, the overall resonance frequency for a groupof three or four units is found to be about 200 cycles per second, asshown in Figure 5. In comparison to this, the resonance frequency of alarge speaker in a large open-backed enclosure will be about 100 cyclesper second. In'the case of such a large speaker, this frequently showsup by a definite boominess in tone quality.

I have found that in order to obtain smooth low frequency response in amulti-cellular speaker assembly it is necessary to employ a number ofsmall speakers and to operate a substantial percentage of the speakerssolely in the range below the speaker resonance frequency (approximately200-cycles per second) while the remainder of the speakers are operatedabove said resonance frequency. In effect, this means building up theresponse in the sound spectrum in the region below the resonancefrequency, attenuating the resonance frequency, and using onlysufficient unitstoreprod-uce in the region above the resonant frequencyto provide the desired amount of medium and high frequency response. Fora multi-cellular unit using small speakers,- such as five-inch speakersin cubical enclosures, arranged as in Figures 1, 3 and 4, or inFigures 8to 11, the low frequency speaker units are driven from an amplifierhaving a low frequency response opposite to that of the speakers,similar to that shown in Figure 6. This latter response curve maybe-obtained by employing a suitable'low pass filter at theinput of thelow frequency amplifier, said filter'being designed to attenuate theinput signal to a very substantial degree in the neighborhood of 200cycles per second and providing substantially complete attenuation at afrequency not far above200 cycles per second, as shown in Figure 6. Theattenuation at 200- cycles per second will then be suflicient tocompensate for the speaker resonance, whereas the gain of theamplifierbelow 200. cycles per second will compensate for the lowspeaker response in this range.

As-shown in Figure '7, the low frequency unitsof..;the;-multi-cellularassembly are driven by an amplifier 18 which isprovided at its input with a low pass filter is having the attenuationcharacteristics above described. The medium and high frequency speakerunits, on the other hand, are driven by an amplifier 20 which isprovided at its input with a high pass filter 2| which is designed tocut off at between 150 and 170 cycles per second, and has relatively lowresponse in the neighborhood of 200 cycles per second, the speakerresonance frequency.

The response of the medium and high frequency portion of the system istherefore relatively low in the region of the resonant frequency of themulti-cellular speaker assembly and is substantially normal above saidregion. The response of the low frequency portion of the system isrelatively high in the region below said resonant frequency and isrelatively low in the region of said resonant frequency. The overallresponse of the system is therefore relatively flat from a very lowfrequency, which may be as low as 20 cycles per second, to the normalupper frequency limit of fidelity of the speakers.

In the low frequency compensation, or baseboost methods heretoforeemployed in the systems of the prior art, no provision has been made forattenuating the resonance frequency of the speaker units, particularlythe low frequency speaker units, and, as a result, the prior artsystems, while extending the response to very low frequency values, haveexhibited strong peaksin response in the region between 30 to, 200cycles. In some cases, thesesystems have beencharacterized by very heavyboomy and barreltone eifects.

Speakers which have a high resonant frequency, such as small commercialspeakers of the fiveinch type, have a natural response curve whichtapers down very rapidly at the low frequency end, as in Figure 5. Inorder to obtain satisfactory low frequency power output from suchspeakers, it is necessary to employ a number of them simultaneously andto operate them from an amplifier having the opposite characteristics,as shown in Figure 6. By employing the electrical arrangement of Figure'7 and using conventional high-pass and low-pass circuits having cut-offvalues approximating those indicated. in Figure 7 at the input of therespective amplifiers 2t! and [8, it is possible to obtain extended lowfrequency reproduction and very smooth low frequency response, usingmerely anumber of thesmall speakers. By mounting the small speakers in arelatively shallow cabinet in cellular fashion, as is shown in Figures1, 3 and 4, the effects of cabinet resonance areminimized, since thecabinet resonance frequency will be close. to and willbe attenuatedinthe same manner as the resonance frequency of the individual speakersthemselves. Figure 8 illustrates an arrangement of cellular speakersemployed with the system of Figure 7, wherein an elongated closedrectangular cabinet 22 is employed, divided-by suitable partition walls'23 into four identical cells. Each cell'contains a small speaker 15,such as a' conventional. fiveinch speaker, mounted on a baille. board [6forming thefront wall of the cell. The last speaker on the right, asviewed in Figure 8, is employed, in the system of Figure 7, to reproducethe medium and high frequencies. The remaining three speakers areemployed to. reproduce, frequencies below the resonant frequency of thespeakers,.i.e., below approximately 200 cycles. per second, and aredriven by an amplifiersuch' as: the. amplifier #8 having the low passinput filtertl-Q.

- I Figure 9 illustrates a substantially square closed cabinet 24 whichis divided by the vertical and horizontal partition walls 25 and 26 intofour square cells, each containing a small speaker l mounted on a bafiieboard [6. In Figure 9, the upper right hand speaker is employed toreproduce the medium and high sound frequencies, while the remainingspeakers are driven only below the speaker resonant frequency, i. e.,below approximately 200 cycles per second, in accordance with thearrangement of Figure 7. Except for the difference in spatialdistribution of the sound output caused by the different spatialarrangement of the respective speakers, the response of the speakerassembly of Figure 9 will be generally similar to that of Figure 8.

In Figure 10, a large shallow closed rectangular cabinet 2'! isemployed, divided by suitable partition walls into an upper centralrectangular cell, designated at 23, and a double row of small cells 29flanking the sides and bottom of central cell 28. The central cell 28has a baffle board 30 on which are mounted the relatively large speakers3|. Each of the small cells 29 has a baffle board IS on which is mounteda small speaker [5. The composite speaker assembly of Figure is drivenby a system such as is disclosed in Figure '7, the large speakers 3|being driven from the output of the medium and high frequency amplifier20, and the small speakers I5 being driven, solely below their resonantfrequency, by the low frequency amplifier I8.

In the arrangement of Figure 11, a first unit, designated at 32, isemployed together with a second unit 33. The unit 32 comprises a closedcabinet formed with a relatively large upper cell 34 and with six smalllower cells 35, arranged in a double vertical bank below the upper cell.Upper cell 34 has a baffle board 36 on which is mounted a relativelylarge speaker 31. Each of the lower cells 35 is provided with a baiiieboard I 6 on which is mounted a small speaker P5. The large speaker 3!is driven from the medium and high frequency amplifier 20 of Figure 7,whereas the small speakers [5 are driven, solely below their resonancefrequency, by the low frequency amplifier IS. The second unit 33comprises a closed rectangular cabinet divided into six square smallcells 38, each cell 38 having a bafile board l6 on which is mounted asmall speaker Ill. The small speakers I 5 of the second unit 33 are alsodriven, below their resonant frequency, from the low frequency amplifierI 8.

The second unit 33 is physically spaced a few feet from the first unit32 and acts to reinforce the low tones, providing a massive soundeffect, especially desirable when the units are employed to reproducethe tones of electronic organs and the like. The sound effect thusobtained is similar to that of large pipe organs, as played in largecathedrals and theaters.

Small composite units such as shown in Figures 1, 8 and 9 are especiallysuitable for home use, as reproducers for radio receivers andphonographs. The larger units, as shown in Figures 10 and 11, areespecially suited for use in theaters, auditoriums, churches, and otherlarge assembly halls.

In each of the composite speaker units above described, th small lowfrequency speakers are operated only below their resonant frequency.Adequate sound output of the low frequencies is obtained by using alarge number of low frequency speakers, as compared with the number ofspeakers employed for the medium and high sound frequencies. Since theeffects of speaker resonance, as well as cabinet resonance, aresubstantially eliminated, the low frequency response is very smooth. Atthe same time, the overall response of the system can be madesubstantially flat from as low as 20 cycles per second to the uppernormal limit of fidelity of the medium and high frequency speakers.Since the units are very shallow, the amount of floor space requiredtherefor is very small. Furthermore, since the speakers are distributedover a large area, the spatial distribution of the sound output is moreuniform than where a single speaker is employed.

While certain specific embodiments of multiple loud speaker units havebeen disclosed in the foregoing description, it will be understood thatvarious modifications within the spirit of the invention may occur tothose skilled in the art. Therefore it is intended that no limitationsbe placed on the invention except as defined by the scope of theappended claims.

What is claimed is:

l. A sound reproducing system comprising a relatively shallow closedhousing, means dividing the housing into a plurality of cells, each cellhaving a baffle board as its front wall and being provided with a loudspeaker located in the cell and mounted on said bafile board, certain ofthe speakers being similar and having natural fundamental resonantfrequencies of approximately 200 cycles per second, a first amplifier,means connecting said certain speakers to the output of said firstamplifier, a second amplifier, means connecting the remainder of thespeakers to the output of said second amplifier, and 7 means wherebysaid first amplifier passes only frequencies below 200 cycles persecond.

2. A sound reproducing system comprising a relatively shallow closedhousing, means dividing the housing into a plurality of identical cells,each cell having a bafile board and being provided with a relativelysmall loud speaker located in the cell and mounted on said baflle board,the speakers being substantially identical and having a naturalfundamental resonant frequency in the neighborhood of 200 cycles persecond, a first amplifier, means connecting certain of the speakers tothe output of said first amplifier, a second amplifier, means connectingthe remainder of the speakers to the output of the second amplifier,means whereby the first amplifier passes only frequencies below 200cycles per second, and means whereby the second amplifier passes onlyfrequencies above 200 cycles per second.

3. A sound reproducing system comprising a small loud speaker, a largeloud speaker, audio input means, means connecting said audio input meansto said loud speakers, means limiting the input to the small loudspeaker to frequencies below the natural fundamental resonant frequencyof said small loud speaker, and means limiting the input to the largeloud speaker to frequencies above the natural fundamental resonantfrequency of said small loud speaker.

4. A sound reproducing system comprising a first loud speaker, firstaudio input means, means connectnig said audio input means to said firstloud speaker, a second loud speaker, said loud speakers beingsubstantially identical, second audio input means, means connecting saidsecand audio input means to said second loud speaker, and means limitingsaid first audio input means to frequencies below the naturalfundamental resonant frequency of the loud speakers.

5. A sound reproducing system comprising a first loud speaker,- firstaudio input means, means connecting the first audio input means to saidfirst loud speaker, :a second loud speaker, said loud speakers beingsubstantially identical, second audio input means, means connecting saidsecond audio :input means to said second loud speaker, means limitingsaid first :audio input means-to frequencies below the naturalfundamental resonant frequency of the loud speakers, 'andmeans limitingthe secondaudio input means to frequencies above said naturalfundamental resonant frequency.

-6. in combination, a multicellularxspeaker assembly comprising anumber-of speakers mounted in individual cells, means driving asubstantial percentage of the speakers mainly in the range below theirnatural resonant frequency, *means driving the remainder of the speakersmainly in "the range above said resonant frequency, and meansattenuating said resonant frequency in the input to all ofsaid speakers.

' 7. In combination, a 'multicellular speaker assembly comprising anumber of small speakers mounted in individual cells, means driving asubstantial percentage of the speakers mainly in the range below theirnatural resonant frequency, means driving the remainder of the speakersmainly in the range above said resonant frequency, and means attenuatingsaid resonant frequency in the input to all of said speakers, wherebysmooth extended low frequency response is obtained for the speakerassembly with- -'out emphasis of said resonant frequency.

8. In combination, a multicellular speaker a's- 'sembly comprising anumber of speakers mounted in individual cells, a first amplifier havinga low frequency response substantially opposite to that of the speakers,means drivingly connecting said first amplifier to a substantialpercentage of the speakers, means substantially confining saidlowfrequency response to frequenciesbelow the natural fundamental resonantfrequency of said percentage of the speakers, a second amplifier, meansdrivingly connecting said second amplifier to the remainder of thespeakers, and means whereby said second amplifier passes onlyfrequencies above the natural resonant fundamental frequency of thespeakersdriven by thefirst amplifier.

:9. In combination, .a multicellular speaker assembly comprising anumber-of speakers mounted in individual cells, a first amplifier, meansdrivingly connecting said first amplifier to a substantial percentage ofthe speakers, means whereby said first amplifier passes only frequenciesbelow the fundamental resonant frequency of the speakers and attenuatessaid fundamental resonant frequency, :a second amplifier, meansdrivingly connecting said second amplifier to the remainder of .thespeakers, and means whereby said second amplifier passes onlyfrequencies above the fundamental resonant frequency of the speakersdrivenby the first amplifier.

10. In combinatioma multicellular speaker assembly comprising a smallspeaker and a large speaker mounted in individual cells, the largespeaker having a natural resonant frequency substantially below that ofthe .small speaker, means driving the small speaker mainly in the :rangebelow the resonant frequency of the small speaker, and means driving thelarge speaker solely. in the range above the resonant frequency :of thesmall speaker, whereby the low frequency response of the system isprovided by the small speaker, the natural resonant response of thelarge speaker is eliminated, and the medium and high frequency responseof the system is provided by the large speaker.

JOHN E. PARKER.

REFERENCES CITED The following references "are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,877,992 Seabert Sept. 20,19321,915,954 Scofield June 27, 1933 1,931,235 Nicolson Oct. 17, 19332,093,076 Engle Sept. 14, 1937 2,122,010 Savage June 28, 1938 2,143,175Waite Jan. '10, 1939 2,160,112 Van Urk et al May 30, 1939 2,242,556Upton May 20, 1941 2,373,692 Klipsch Apr. '17, 1945

